Re: PATCH] Use -mpreferred-stack-boundary=3 on x86-64 if supported

[Randy Dunlap <rdunlap@xxxxxxxxxxxx>]

On 06/23/2012 09:49 AM, H.J. Lu wrote:

> On Sat, Jun 23, 2012 at 9:17 AM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
>> To keep gcc from paddong the stack to maintain a nonexistent alignment.
>>
>> Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
>>
>>>> This patch uses -mpreferred-stack-boundary=3 on x86-64 if it is
>>> supported.
>>>> I have been running 3.4 kernel compiled with this option for weeks.
>>>
>>> But why?
>>>
>>> All the SSE code in the kernel should adjust manually. And the other
>>> code doesn't need it.
>>>
>>> Besides the entry points do not guarantee alignment.
>>>
>>> For the kernel it would be probably more useful to have a attribute
>>> per function that forces alignment.
> 
> There was an attempt from you to do it in 2007:
> 
> http://lkml.indiana.edu/hypermail/linux/kernel/0708.2/2604.html
> http://gcc.gnu.org/ml/gcc-patches/2007-07/msg01697.html
> 
> But the gcc patch was never checked in.
> 
> 


Some (most) of this explanation needs to be in the patch description.


-- 
~Randy
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